Development of a K-shell x-ray fluorescence measurement of cadmium in bone

Cadmium is known to accumulate in the human body and chronic exposures have been clearly linked to adverse health effects, showing the kidney as the critical target organ. However, there is evidence of an association between extensive environmental exposure to cadmium and alterations in bone/calcium metabolism. Therefore, it is desirable to be able to measure bone cadmium non-invasively in humans. Tibia was selected as a measurement site and source-excited K-shell x-ray fluorescence was investigated both experimentally and computationally. Initially the 88 keV gamma-rays from Cd-109 were used to assess minimum detectable level (MDL) of cadmium in phantoms comprising plaster of Paris (bone) and wax (soft tissue). An MDL of 3-4 mu g g(-1) was achieved for overlying tissue thicknesses of up to 5 mm. Alternative sources were I-125 and Am-241. Monte Carlo simulation showed that the spectral contrast for I-125 would be poor. The 60 keV gamma-rays from Am-241 were more promising, provided that the 26 keV gamma-rays were filtered out. Experiments with Am-241 confirmed that a lower MDL could be achieved. However, the product of MDL and square root of dose (a figure of merit) was not improved. Since effective doses for these source-excited x-ray fluorescence procedures are low (typically of the order of 0.1 mu Sv or less), it may be that lower MDL would be preferred over lower dose. Nevertheless, development continues as a further reduction in MDL is highly desirable. Copyright (c) 2005 John Wiley & Sons, Ltd.